The present invention relates generally to communication systems and, in particular, to geo-location of communication devices.
The idea of geo-location of wireless communication devices, such as mobile telephones, is well known. Current geo-location techniques for wireless communication devices involve employment of the well-known Global Positioning Satellite (GPS) system and/or network-based solutions, such as forward and/or reverse link triangulation techniques. See FIG. 1, which illustrates an architecture for locating mobile-telephone 16 using a plurality of GPS satellites 12 comprising the GPS system and/or a plurality of base stations 14 used in network-based solutions. Note that the term GPS shall include the Global Positioning Satellite system and other geo-location satellite systems.
One drawback with either of the aforementioned geo-location techniques is that altitude estimates are inherently inaccurate. The reason for this inherent inaccuracy is, simply, geometry. Specifically, most of the sources/receivers, i.e., base stations and satellites, tend to be in or near the horizontal plane. To obtain an accurate altitude estimate, one or more (preferably several) sources/receivers should be nearly overhead. Note that a base station or satellite is considered to be in or near the horizontal plane if it is not more than 45xc2x0 above the horizon, as shown in FIG. 1. For network-based solutions, all of the base stations 14 are in the horizontal plane of the local ground level allowing for location fixes in the horizontal position but not in the vertical position. For GPS systems, although one or more GPS satellites 12 may be overhead, most of GPS satellites 12 are near the horizontal plane. Thus, location fixes employing GPS systems are substantially less accurate in the vertical position than in the horizontal position. Furthermore, if fewer than four GPS satellites are visible, determining the vertical position of the receiver is generally impossible, regardless of the satellites"" position in the sky.
Unfortunately, accuracy in determining the location of a mobile-telephone in the vertical position is more desirable than for the horizontal position. For example, if a crime is reported and a set of coordinates (longitude, latitude and altitude) is provided to the police, a horizontal (longitude and latitude) error of tens of meters is largely inconsequential whereas a vertical (altitude) error of tens of meters would lead the police to a wrong floor of a building. Even under optimal conditions, the vertical accuracy of differential GPS receivers, which are currently the best available GPS receivers for determining location using GPS satellite signals, is frequently as poor as tens of meters.
Accordingly, there exists a need for estimating a vertical position or altitude of a communication device more accurately and independently of other measurements of position.
The present invention is a communication device and method for estimating a more accurate vertical position or altitude of a communication device using atmospheric pressure measurements. In one embodiment, the present invention is a first communication device comprising of a pressure sensor for measuring local atmospheric pressure at the first communication device and a transceiver for communicating with a second communication device, wherein the transceiver may be operable to receive barometric calibration information for calibrating a local atmospheric pressure measured at the first communication device and/or to transmit the measured local atmospheric pressure to the second communication device. The first communication device may further comprise a processor for estimating an altitude using the measured local atmospheric pressure and received barometric calibration information. The received barometric calibration information being transmitted to the communication device by the second (or a third) communication device which may be a part of a wireless communication network, such as a cellular network. The second communication device being operable to determine the barometric calibration information using a barometer or pressure sensor, to transmit the barometric calibration information in a manner indicating to the first communication device that the information being received is barometric calibration information, and/or to receive local atmospheric pressure measurements from the first communication device.
In another embodiment, the present invention is a method comprising the steps of measuring local atmospheric pressure using a pressure sensor at a communication device, and estimating an altitude of the communication device using the measured local barometric pressure and barometric calibration information corresponding to another atmospheric pressure measurement at a known elevation near the communication device.